Foscarnet and ganciclovir have been used for the treatment of CMV retinitis. Both have been shown to be effective, but recurrence is common and some patients continue to lose vision despite treatment. 1-(S)-(3-Hydroxy-2-phosphonylmethoxypropyl)-Cystosine Dihydrate (HPMPC, Cidofovir) is a nucleotide analog with potent activity herpes viruses. Limited clinical studies have shown renal toxicity to be the most common adverse effect.